The present invention relates to a technique of suppressing electromagnetic waves generated within an apparatus provided with a units of wireless communication, and in particular to a technique of reducing electric field noise generated within a printed circuit board or an information processing apparatus.
In an information processing apparatus, as LSIs used in the apparatus becomes high-speed in their clocks and high-density in their mounting, noise generated within the apparatus increases. In an information processing apparatus or the like having a units of wireless communication, noise generated within the apparatus causes to deteriorate the wireless communication performance such as reduction of the data throughput or of the communication distance between the information processing apparatus and an external source of the communication data (ex. a radio antenna).
FIG. 16 shows an example of results of investigation on the effects of noise within an apparatus on the communication performance. The horizontal axis indicates a communication distance (m) between two communication apparatuses, and the vertical axis indicates a bit error rate (%) of the data. This figure shows a case (a dotted line a) where there exists interference by noise of a CPU or the like, and a case (a solid line b) where there does not exist interference by noise, in a PC mounted with a wireless unit using a 2.4 GHz band. In the case where no interference exists, the communication distance at the error rate 0.1% is about 100 m, while, in the case where interference exists, the communication distance is only about 20 m, i.e., 20% of the former case. Thus, when there is a noise source within an information processing apparatus having a wireless communication function, the noise source deteriorates the wireless communication performance of the apparatus.
As a method of reducing the effects of a noise source on a wireless communication function, there is a proposed mounting method in which a noise source on a circuit board is distant to a wireless communication board, as disclosed in Japanese Application Patent Laid-Open No. 10-268988, “Portable Information Apparatus with Wireless”.
However, in this method, a board having a wireless function should be located in a sufficient distance from a noise source on a circuit board, and sometimes this becomes an obstacle to miniaturization of an information processing apparatus. Thus, it is difficult to apply this method, for example, to a cellular phone having a small-sized chassis.
The present invention has been taken the above situation into consideration. One advantage of the present invention is to provide a circuit board that can reduce effects of noise on a wireless communication board mounted on the circuit board, even when a noise source is not distant to the wireless communication board.
Another advantage of the present invention is to apply the above-mentioned circuit board to an information processing apparatus having a wireless communication function, and to provide a small-sized information processing apparatus having an improved wireless communication throughput and an increased communication distance.